Priority is claimed to Korean Patent Application No. 2004-3237, filed on Jan. 16, 2004, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Disclosure
The present disclosure relates to a method of forming a nano-sized magnetic tunnel junction (MTJ) cell without a contact hole, and more particularly, to a method of forming a nano-sized MTJ cell in which a contact is formed in the MTJ cell without forming a contact hole.
2. Description of the Related Art
Flash memory is a type of nonvolatile memory that has an advantage in that data recorded in the memory is preserved even if power is turned off. However, the recording speed of data in flash memory is approximately one one-thousandth that of DRAM, and flash memory also has high power consumption. Also, there is, to some extent, a limit of data erasing and writing times. Therefore, research has gone into the advantages of the DRAM and the flash memory, that is, reading and recording at a high speed, low power consumption, and data preservation even if power is turned off. As a result of the research, ferroelectric RAM (FeRAM), ovonic unified memory (OVM), and MRAM have been introduced as non-volatile memory.
Magnetic random access memory (MRAM) is non-volatile memory in which a memory cell includes a magnetic tunnel junction (MTJ) that stores information using a tunneling magneto resistance effect. Referring to FIGS. 1A and 1B, an MTJ includes an insulating layer 200 (tunnel barrier layer) interposed between two ferromagnetic layers 100 and 300. Data stored in the MTJ depends on the direction of magnetization, i.e., whether the direction of the magnetization either same or opposite. That is, as depicted in FIG. 1A, if the directions of magnetization are parallel, the tunnel resistance of the insulating layer 200 (barrier layer) interposed between the two ferromagnetic layers 100 and 300 is minimized, and the MTJ is in a “1” state. On the other hand, as depicted in FIG. 1B, if the directions of magnetization are anti-parallel, the tunnel resistance of the insulating layer 200 is maximized, that is, the MTJ is in a “0” state. By utilizing these unique characteristics of the MTJ, the MTJ can function as a memory cell. Hereinafter, a memory cell including the MTJ will be called an MTJ cell for convenience.
FIGS. 2A through 2H are cross-sectional views illustrating a conventional method of forming an MTJ cell.
Referring to FIG. 2A, an MTJ layer 220 and a hard mask layer 230 are sequentially formed on a substrate 10. After stacking a photo-resist 232, on a portion of the hard mask layer 230 in which an MTJ cell will be formed, the hard mask layer 230 is dry etched using the photo-resist 232 as an etch mask. Referring to FIG. 2B, the photo-resist 232 is then removed.
Next, a remaining portion of the hard mask layer 230 and a portion of the MTJ layer 220 are dry etched (FIG. 2C), and then an insulating layer 240 is deposited on the resultant product (FIG. 2D). Then, referring to FIG. 2E, a mask layer 235 for forming a contact hole 260 is coated on the insulating layer2 40, and then, a contact hole is patterned by performing lithography using a Kr stepper. Then, referring to FIG. 2F, central portions of the insulating layer 240 and the photo mask 235 are etched, thereby forming the contact hole 260 in the middle of the MTJ cell. Finally, the mask layer 235 is removed (FIG. 2G) and a metal layer 250 is coated on the resultant product (FIG. 2H) to complete the manufacturing of the MTJ cell.
A memory cell formed in this manner can record and reproduce at high speeds and has lower power consumption, and an unlimited number of data corrections can be made.
However, for practical applications, high integration of the MRAM is essential. Therefore, the MTJ cell must have a width less than 100 nm. However, it is difficult to manufacture an MTJ cell having a width less than 100 nm using the present technique. If the MTJ cell is manufactured according to a conventional method, a contact has to be formed after forming a contact hole having a diameter much less than 100 nm in the MTJ cell with a width of 100 nm. Thus, it is impossible to form an MTJ cell having a width less than 100 nm using conventional methods. The size of conventional MTJ cells developed is no smaller than 400×800 nm, which is much greater than the required size for high integration. That is, the applicability of conventional MRAM is very low. Moreover, when an MTJ cell is formed according to a conventional method, a resistance of the contact is high since the contact hole is very small, thereby causing errors during recording and reproducing data and increasing power consumption.